In order to satisfy the demand for the electronic devices to be small sized and consume less power, IC chips that are the main component of the electronic devices are becoming smaller and smaller. Currently, the size of the actually distributed IC chips (bare chips) satisfies well such demands. However, the size of the electronic devices is decided by the size of a package wrapping the IC chip, rather than the size of the IC chip itself.
On the other hand, for the semiconductor manufacturers, it is preferred, in view of easy handling in the test process and enabling cost reduction, to supply the semiconductor devices in the form of a mold-sealed package by pulling a lead of the chip, rather than supplying semiconductor devices in the form of a bare chip or a flip chip.
Under such a background, as the IC chips, a surface mounting type package with the packaging density increased in the height direction is becoming particularly predominant, and is provided in various forms such as SOP (Small Outline Package), QFP (Quad Flat Package) and BGA (Ball Grid Array).
With the introduction of various surface mounting type electronic parts including such IC chips, miniaturization and high integration of the electronic circuit board are planned, thereby increasing the number of parts arranged on the same circuit board. Normally, mounting of these electronic parts on the printed circuit board, that is, electric connection between a predetermined electrode pad portion on the printed circuit board and the electronic parts is realized by so-called reflow soldering processing.
The reflow soldering processing is achieved by a series of flow comprising: a solder printing step of printing a cream solder on an electrode pad portion which performs electric connection with the electronic parts; a mounting step of mounting the electronic parts so that an electrode pin or bump is located on the printed solder; and a reflow step of performing electric connection between the electronic parts and the printed circuit by melting and fixing the printed solder, on the printed circuit board having a predetermined circuit pattern formed thereon.
The solder printing step, mounting step and the reflow step are respectively performed by a printer, a mounter and a reflow apparatus, and these apparatus have a conveyor, to thereby carry the printed circuit board processed by own apparatus out to the apparatus on the subsequent stage. Among these apparatus, particularly, the reflow apparatus needs to heat the printed circuit board and the electronic parts in order to melt the solder, and hence its main function is to control the heating.
FIG. 11A and FIG. 11B are diagrams that explain the construction of a conventional reflow apparatus and the temperature profile. As shown in FIG. 11A, the reflow apparatus sequentially carries a surface-mounted circuit board 700 to a preheating chamber, a main heating chamber and a cooling chamber by a conveyor 701, to thereby perform reflow soldering with respect to the surface-mounted circuit board 700. The surface-mounted circuit board 700 stands for a printed circuit board in the state of having various electronic parts mounted thereon by the mounter, after having been solder printed by the printer.
At first, the surface-mounted circuit board 700 carried to the preheating chamber is subjected to soaking only by a hot air blower 702, after having heated the surface-mounted circuit board 700 by using a heater 703 and the hot air blower 702. During this preheating, the board portion of the surface-mounted circuit board 700 reaches the soaking temperature as shown by a solid line 801 and the parts on the surface-mounted circuit board 700 reaches the soaking temperature as shown by a dotted line 802 in FIG. 11B.
Subsequently, the surface-mounted circuit board 700 carried to the main heating chamber is subjected to soaking only by the hot air blower 702, after having heated the surface-mounted circuit board 700 to a high temperature by using the heater 703 and the hot air blower 702. During this main heating, the board portion and the parts of the surface-mounted circuit board 700 respectively reach the soaking temperature as shown by the solid line 801 and the dotted line 802 in FIG. 11B. Thereby, the solder printed on the surface-mounted circuit board 700 melts, to thereby join the parts and the printed circuit. Then, the surface-mounted circuit board 700 is cooled in the cooling chamber, to thereby fix the melt solder, and as a result, the electric connection between the parts and the printed circuit is obtained.
As described above, with the reflow apparatus, in order to perform temperature control in accordance with the temperature profile as shown in FIG. 11B, that is, to accurately perform temperature control, it is necessary to accurately determine the speed of the conveyor 701, the heating temperature of the heater 703, and heating conditions such as the hot air temperature of the hot air blower. The heating conditions include heating characteristic data peculiar to the reflow apparatus, and data regarding the surface-mounted circuit board 700 involving the kind, the size and the physical property of the board, the kind, the size and the physical property of the parts mounted on the board.
However, since the setting operation of these heating conditions is complicated and time-consuming, the actual temperature control by the reflow apparatus has been heretofore performed, in many cases, by repeating operations of first setting heating conditions under which an object to be heated is assumed to reach a desired temperature with respect to the reflow apparatus by an operator, based on his experience and intuition, and adjusting again the heating conditions from the results obtained by the setting (hereinafter referred to a “first method”).
Moreover, as another method, there is a method in which the heating characteristic data of the reflow apparatus, and the size and the physical property data of an object to be heated are input to the reflow apparatus and other apparatus to calculate the heating conditions under which the temperature of the object reaches to a desired temperature, and the heating conditions are set to the reflow apparatus (hereinafter referred to a “second method”).
In the first method, however, since skill and experience are required for setting the heating conditions, only an expert can realize this method. With the second method, since an optimum setting value is calculated from the heating characteristic data of the reflow apparatus input beforehand and the characteristic data of the object, the operator need not be an expert. However, if more accurate calculation is to be performed, much data of the object is required, and not only the input work becomes complicated, but also much time is required for that calculation. Therefore, it is not possible to quickly shift to the actual reflow soldering step, and hence it is not practical to incorporate this method in the actual operation.
Furthermore, the current eutectic solder is an alloy containing lead in about 37% or more, and the existence of lead becomes a big problem in dumping and recycling the electronic parts. Under this situation, there is a desire to use lead-free solder. However, since the lead-free solder has a higher melting temperature than the eutectic solder, it is necessary to increase the temperature for heating the surface-mounted circuit board in the reflow apparatus, causing a problem in that the temperature control must be performed more accurately so as not to exceed the heat resistant temperature of the parts.